Mechanical plugs of various types are well known expedients for plugging conduits and other passageway defining means. Mechanical plugs, however, present problems when utilized to form a water stop in conduits having electrical cables therein. First of all, cables must normally be precisely centered relative to the conduit to permit insertion of a mechanical plug into the conduit. This condition does not always exist.
Furthermore, when a plurality of cables are disposed in a conduit, many irregular shaped voids will be formed in the passageway cross section, voids which mechanical plugs are often unable to fill. For example, voids created by concentric neutrals on electrical cables cannot be effectively sealed with the mechanical plug approach. Also, mechanical plugs can exert a very high degree of pressure against cables within a conduit. This can "neck-down" or even fracture insulation, especially when high heat conditions exist, which can cause shorting. Also, heavy cables, can, over time, distort the plug and break the seal.
Mechanical plugs present problems even when used in conduits or other forms of passageway defining means not housing cables if the passageway is out of round or irregular shaped. Expansion of a mechanical plug in such an operational environment will not completely seal the passageway and thus will allow leakage.
Polyurethane foams have been used to form plugs in conduits. However, such foams can create hazardous conditions. For example, when exposed to flame, such foams can generate poisonous gases. Also, at least one constituent material of polyurethane has been shown to be carcinogenic.
U.S. Pat. No. 4,751,947, issued June 21, 1988 to Phillip G. Landers, discloses a system for plugging a conduit wherein a liquid epoxy foam system is foamed insitu within a conduit to form a plug. However, epoxy foams are often not water compatible and are unable to create a fluid-tight barrier within a conduit which has running water therein or is otherwise characterized by high-moisture conditions.
U.S. Pat. No. 4,773,792, issued Sept. 27, 1988 to Phillip G. Landers, relates to a system for stabilizing structural elements wherein a liquid epoxy foam system is foamed insitu between the structural elements. The foam system is in a flexible container and some of the foaming agent migrates through the container wall to form a bond with a structural element. This epoxy foam based system is inappropriate and inadequate for use in wet passageways to form a plug.